One of the great benefits of the Internet is that many millions of users have access to the shared information and communication of the World Wide Web. However, open access to all forms of information or communications is not always appropriate. For example, many schools and businesses provide Internet access for their students and employees. The school or business is, at least in part, responsible for dissemination of information within that organisation and is usually under an obligation to prevent circulation of racist, sexist or other abusive materials. This is just one example situation where there is a strong need for a measure of control over Internet access. Another example is a home environment, where parents may wish to prevent their children accessing adult-oriented web pages. Other examples include public spaces such as libraries, Internet cafes or public Internet kiosks.
Several systems are available in the related art to monitor or control access to the Internet. For example, U.S. Pat. No. 5,884,033 (Duvall et al) discloses a client-based filtering system that compares portions of incoming and/or outgoing messages to filtering information stored in a database, and determines an appropriate action, such as whether to ALLOW or BLOCK transmission of messages. An update server is accessible over the Internet for updating the database.
US2003/0088577A1 (Thurnhofer et al) discloses a method of generating a database having a relatively large number of data items classified into a relatively small number of categories, using a form of directed graphs. This database was been developed specifically for compactly and efficiently storing a large number of URLs and associated category codes. However, the database must be completely rebuilt at each revision to add new URLs or amend the categorisation.
The filtering systems and database structures of the related art encounter a variety of different demands. For example, such database structures are often required to be relatively compact so as to minimise a size of the database. However, it is also desired for the system to access the database structure at high speed. Further, it is desired to update the database at frequent intervals. Further still, it is desired to protect the security of the database. These and other problems in the related art are addressed by some of the exemplary embodiments of the invention, and will now be discussed in more detail.